So, I tired once before to set my idle using the FSM method but my car would not stay running in order to do it.

I decided today to try and set the idle by using winaldl and using the IAC counts but got a little nervous about the whole process and stopped.

My idle is not too bad, once warm it will hop around a little from 540-620 when stopped at a light or what not but I would like it a little smoother.

In Winaldl the IAC is reporting 78. Am I to understand that I need to be turning the adjustment screw to the right until this number gets down between 20-30 and then adjust the TPS to .54 at the new throttle position? It seems in order to get that IAC number that low I am going to be opening up the throttle quite a bit. FYI I have cleaned the throttle and installed a new IAC.

I had to remove the metal plug, how would this get so out of whack from the factory original setting or is 78 not as much as I think? The 78 was also the reading with my old IAC as well, putting in the new IAC didn't change anything on that front.

At idle my BLM is reading 108, does this reading coupled with the IAC number mean anything?

Any who, any advice/insight would be greatly appreciated.

My guess is I need to open up my throttle using the screw and the opening being so small is why my car wouldn't hold idle trying to use the FSM method.... sound right?

 

You need to do this adjustment when the engine is hot. Otherwise the ECM will be in "fast idle" mode.

I like my IAC count around 50 at idle, hot. That gives the ECM room to adjust the idle. If you set the IAC count too low then the ECM could run out of adjustment (IAC count goes to zero and obviously can't go lower than that).

Your BLM of 108 is at the limit. You have a problem. You are running rich. It's possible the ECM has opened the IAC (higher count) to add more air to try to compensate for the rich AFR. That will affect the idle RPM and cause problems.

Do you have stock sized injectors? Stock FPR (Fuel Pressure Regulator)? Ruptured FPR diaphragm? Bad O2 sensor?

 

I was doing this when the engine was warmed up... however, It seems my data connection was causing fast idle though I wouldn't think it should since it should be jumper-ed for just data logging and the service light was not on... but the minute I pulled the data cable the idle fell back down to the correct range.

I have original injectors, original FPR, FPR is functioning correctly, fuel pressure is right, O2 sensor looks to be working correctly as well looking at the data stream. I do think the car has an aftermarket chip, though I have not actually taken a look. My fan kicks on at 175-178 temps which makes me believe it might have a non stock chip.

When data logging and driving my BLM's rise, I attached a pic.

Honestly the car runs great and I am getting good mileage, it just seems to run rich at idle. It looks like the most correction is happening at idle at low MAF air flow numbers.

 

Oh, and just to clarify, the IAC number I see in Winaldl is the number I should get down to 50?

I might do that and get more air coming in the TB at idle and reset the TPS to .54 at that position.

 

Your car is rich at idle and as you noted, the screw doesn't move and there's no reason to move it now - there's only one temp, one barometric pressure and one relative humidity from which everything else works and the guys who designed it figured that out. It would help to know the Year and whether or not this is a new problem, but you need to fix the rich condition. The IAC is simply adding air to keep it running. Easy to diagnose by following the Code 45 Chart but look at the Coolant Temp Sensor reading when it's cold and make sure it matches ambient and then when it's warmed up, a couple degrees from the reading on your Display. Also clamp off the Canister hose and see if that leans it out. Disconnect the MAF to see if it's better. From there, you might suspect a rich or leaking injector and it's maybe a good idea to do what we use to do from the onset and that's to check compression.

 

I had a compression and leak down test soon after purchasing, results came back with no issues found.

It's an 85.

I am not getting a code 45.

I dunno, it's not like I can't live with the slightly rough idle and the car performs just fine, I should probably just let it go for now until an actual code occurs or I have an actual problem starting or running the car.

AS far as checking the canister purge system, where would I clamp it to see if it leans out?

 

It doesn't matter that there isn't a Code. The diagnostic aids shown in the Chart are used for any engine (with electronic fuel injection) that has a rich condition. That's where the Service Manuals will take you under the topic Rough, Unstable or Incorrect Idle/Stalling.

Follow the hose from the Canister to the Throttle Body. Clamp that hose (or you could remove it and plug the hole at the Throttle Body with a large vacuum cap).

 

Fuel Pressure Regulator Vacuum Line

 

I have checked the FPR Vacuum line, no gas.

I will try the Canister thing though... I mean it is 29 years old and is something I have not checked.

Whatever the issue is it's not effecting performance or reliability.

 

Look For Blockage On The Vacuum Line

 

If the cable has a 10K resistor in it the ECM will set the idle to 1000 RPM, among other things (it affects the spark advance too). Some cables have a switch for the 10K resistor. Take it out if you can.

My experience is that the throttle body and linkage wear, settle or whatever over time and you need to do a minimum idle adjustment:

http://forums.corvetteforum.com/1570563689-post1.html

 

Mine does and is jumpered, I will take it out.

I tried to do it the normal way and the car would not stay idling for me to go adjust (I guess I could manipulate the TB myself while adjusting of course). Wouldn't this be a good sign that the TB needs adjusting and opened a little more? Of course I understand that maybe that isn't the issue and it is too rich to keep running right? Basically if I do the procedure and it takes opening the TB up so much that the car will only run at high idle (1K+) then I know the rich condition is a bigger deal right because the lack of the IAC involvement to compensate while doing the procedure?

That is to say the car should Idle without IAC use at the recommended 450RPM in drive if everything is as it should be? The IAC then introduces air so the car idles higher than the 450 (I hear people like 600-700, mine is bouncing between 550-620) and controls air to keep the idle steady.

If I want a good idle between 600-700 how high should I set the RPM during the procedure?

Thanks everyone again for the advice!

 

Idle specs: Actual Idle 100 +/- RPM's from Targeted in Park/Neutral; 50 +/- RPM's from Targeted in Drive. There was a PROM recall on the '85, but those cars were zeroing out the IAC and stalling. Yours doesn't seem to have that problem. There is more than just a fuel soaked Canister that will add too much fuel - such as a MAF that reads the incorrect air flow which is why you should try it without it to see if it smooths out. You could also pull plugs to see if there's a rich cylinder, but the electrodes are self cleaning once under way, so that test isn't as fool proof as it once was. Better to cut up some 1/4 inch vacuum hose about an inch in length and insert it between each plug wire and the distributor tower/post. Touch the vacuum hose with a grounded test light to kill the cylinder while monitoring RPMS. Any cylinder that doesn't drop the same as all the others is the problem.

 

My car was dying at idle. I always thought the mechanical idle was sealed for a reason and would never need to be adjusted. Doing the minimum idle adjustment fixed my problem.

When I started doing the adjustment the engine would not idle. It would start but immediately die. I had to turn up the idle with the adjusting screw to get it to stay running when I started it. After I got it to stay running I set the idle RPM per the procedure.